This invention relates generally to radio frequency 1.030 switches adapted for coupling one port thereof to a selected one of a pair of ports thereof and more particularly to switches of such type operative at radio frequencies above 1,000 megahertz (MHz).
As is known in the art, it is frequently desirable to transfer power from one electrical circuit to a selected one of a plurality of electrical circuits. Such a power transfer may be accomplished using various types of switches. One such type of switch for providing such power transfer relies on the "making and breaking" of mechanical contacts for its operation. Such switches may operate satisfactorily at radio frequencies greater than 1,000 MHz, but, over a period of time, tend to have their contacts wear, resulting in faulty or intermittent operation.
A second type of switch which avoids the "making and breaking" of mechanical contacts is a so-called "capacitively coupled" switch. While such type of switch has been found satisfactory when operating at radio frequencies less than 1,000 MHz, such switches become impractical when required to operate at higher frequencies because of their extremely small size and relatively high cost. Further, at such higher frequencies it is generally critical that the impedance provided by the switch to the power, as such power passes from an input port to an output port, be uniform in order to assure that maximum power is transferred from the input port to the output port. With a "capacitively coupled" switch it is generally difficult to obtain this desired impedance characteristic, especially where it is desired that the switch have at least an octave operating bandwidth.
As is further known in the art, radio frequency energy having frequencies greater than 1,000 MHz may be coupled between a pair of transmission lines using offset parallel coupled strip transmission lines as described in the article by J. Paul Shelton, Jr. entitled "Impedance of Offset Parallel-Coupled Strip Transmission Lines" published Jan. 1966 in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-14, No. 1. With such coupling technique two strip conductors, of proper design, disposed in a dielectric between a pair of ground planes, will effectuate the desired maximum power transfer, over an octave bandwidth, when the strip conductors are oriented precisely (to an accuracy in the order of .lambda./200, where .lambda. is the wavelength of the normal operating frequency of the coupler) with each other. While such an "offset" coupler has been found effective when the strip conductors are fixed in their relative position, the technique of offset coupling has, heretofore, not been extended to switches where the strip conductors are required to move one with respect to the other because of the difficulty in obtaining the precise orientation required of the strip conductors as mentioned above.